In many applications, circuitry formed on different substrates needs to be interconnected. One example would be the electrical interconnection of a monolithic integrated circuit chip with another substrate, such as a printed circuit board or a thin polyester sheet having circuit traces printed thereon. For example, U.S. Pat. No. 5,612,513; U.S. Pat. No. 5,987,739; and U.S. Pat. No. 6,031,459 disclose wireless communications devices wherein a semiconductor chip is conductively bonded to a thin polymer sheet having conductive traces including antenna fabricated thereon. Each of these documents is herein incorporated by reference.
Such documents disclose electronic identification systems typically comprising two devices which are configured to communicate with one another via a wireless medium. Such communication systems can be used in various identification functions and other applications. An interrogator is configured to output a polling signal which may comprise a radio frequency signal including a pre-defined code. The transponders of such a communication system are operable to transmit an identification signal responsive to receiving an appropriate command or polling signal. Such communication systems are usable in identification applications such as inventory or other object monitoring. For example, a remote identification device is attached to an object of interest. Responsive to receiving the appropriate polling signal, the identification device is equipped to output an identification signal. Generating the identification signal identifies the presence and/or location of the identification device in the article or object attached thereto.
The majority of the circuitry which carries out these functions is typically fabricated into a monolithic integrated circuit chip. This chip is then bonded to another thin polymer sheet atop which conductive printed thick film ink has been fabricated. The ink includes traces defining an antenna for the device and battery and ancillary circuit interconnections for the monolithic chip effective to achieve the desired functioning.
A preferred method by which the chip is connected to the circuitry of the polymer sheet is by first fabricating conductive polymer bumps on all the desired connection locations, typically referred to as bond pads, on the semiconductor chip. Example material for the conductive polymer bumps is conductive epoxy, such as conductive epoxy part number 116-37A, mixed with hardener B-187 in the proper ratios. Both materials are available from Creative Materials, Incorporated, located in Tyngsboro, Mass. Such bumps are applied by any suitable means over the bonding pads and allowed to essentially completely cure. Thereafter, the secured bumps are bonded with the same or similar conductive epoxy material which has been applied over polymer sheet circuitry where the connection is desired. Thus, a conductive interconnection is made between the chip and other substrate circuitry, with the interconnection also serving as an adhesive interconnect between the chip and thin sheet substrate.
In certain instances, the degree of adhesion achieved in the prior art is less than desirable. Such can accordingly result in less than desired conductivity in the interconnect between the chip and conductive traces of the polymer sheet.